"I am sick to the heart to hear of the poisoning of the Marsh Pride lions, and horrified to think of the pain they suffered as they died," said Saba Douglas-Hamilton, a Kenyan conservationist and television presenter who worked on Big Cat Diary.

Jonathan Scott, a zoologist and one of the show's original presenters who has been following the Marsh Pride for nearly 40 years, lamented the poisoning as the "end of an era".

Among the dead lions was 17-year old female Bibi, who had become something of a celebrity during the TV series' long and hugely popular run from 1996-2008.

The BBC crew said Bibi was found "lying on her side, foaming at the mouth, fitting and panting" before she died.

Conservationists first noticed something was wrong on Sunday morning when some of the lions, "were acting strangely collapsing and suffering from spasms," according to a statement from the David Sheldrick Wildlife Trust which funds a mobile veterinary unit in the reserve.

Local cattle-herders who frequently bring their animals into the Masai Mara National Reserve to graze are suspected of the poisoning.

"Tens of thousands of cattle encroach into the reserve every night when visitors are safely out of sight," said Scott.